In motor vehicles of this type, in which the rear axle is also actively steered to improve steerability in tight curves and especially during parking, the rear wheels are only steered in the same direction, with the steering of the rear wheels either depending or not depending on the steering of the front wheels.
All that can be done with such motor vehicles, therefore, is to reduce the turning circle. Improvements in steering characteristics in long, gentle curves, as often occur especially during highway driving, cannot be achieved in this manner.
EP-OS 0221547 discloses a steering angle adjustment device for a steerable front axle in which the front wheels, retained on the front axle beam by control arms, are steered in the usual way with tie rods and steering arms. Provided to mount the control arm on the front axle beam are first control arm bearings accommodating a slight horizontal pivot motion and second control arm bearings located along the long axis of the vehicle, offset from the first control arm bearings, and serving as hydraulic positioning elements, by means of which the linking points of the wheels to the axle beams can be shifted outward or inward with respect to the long axis of the vehicle.
With this known front axle, the steering angle of the front wheels, namely, the angle through which the front wheels are pivoted out from their straight-ahead position during steering, is corrected by the fact that the linking points of the front wheels on the control arm bearings are shifted by the steering angle set by the standard steering system and by the lateral forces occurring at the front wheels, so as to optimize the steering angle of the front wheels in terms of slip angle and cornering force.
With this known device for adjusting the front wheels' steering angle, the latter can be optimized for good steering characteristics, but no additional influence on the steering characteristics of the motor vehicle can be achieved with this known device.
On the other hand, the problem on which the invention is based is that of creating a motor vehicle of this type with all-wheel steering, in which, in addition to a reduced turning circle, steering characteristics at small steering angles and tracking are also improved.